Provide a sanity check during PyThreadState_DeleteCurrent() and PyThreadState_Delete() to avoid an infinite loop when the tstate list is messed up and has somehow becomes circular and does not contain the current thread. I don't know how this happens but it does, *very* rarely. On more than one hardware platform. I have not been able to reproduce it manually. Attaching to a process where its happening: it has always been in an infinite loop over a single element tstate list that is not the tstate we're looking to delete. It has been in t_bootstrap()'s call to PyThreadState_DeleteCurrent() as a pthread is exiting.